[PATCH v6 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL

AKASHI Takahiro
2014-08-21T08:57:47Z

To allow tracer to be able to change/skip a system call by re-writing
a syscall number, there are several approaches:

(1) modify x8 register with ptrace(PTRACE_SETREGSET), and handle this case
later on in syscall_trace_enter(), or
(2) support ptrace(PTRACE_SET_SYSCALL) as on arm

Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
tracer as well as that secure_computing() expects a changed syscall number
to be visible, especially case of -1, before this function returns in
syscall_trace_enter(), we'd better take (2).

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
arch/arm64/include/uapi/asm/ptrace.h | 1 +
arch/arm64/kernel/ptrace.c | 14 +++++++++++++-
2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 6913643..49c6174 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -23,6 +23,7 @@

#include <asm/hwcap.h>

+#define PTRACE_SET_SYSCALL 23

/*
* PSR bits
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 0310811..8876049 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1077,7 +1077,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
long arch_ptrace(struct task_struct *child, long request,
unsigned long addr, unsigned long data)
{
- return ptrace_request(child, request, addr, data);
+ int ret;
+
+ switch (request) {
+ case PTRACE_SET_SYSCALL:
+ task_pt_regs(child)->syscallno = data;
+ ret = 0;
+ break;
+ default:
+ ret = ptrace_request(child, request, addr, data);
+ break;
+ }
+
+ return ret;
}

enum ptrace_syscall_dir {
--
1.7.9.5